1. Field of the Invention
The invention relates to a zoom lens and a cam frame thereof
2. Description of the Related Art
Typically, a cam frame of a zoom lens has a plurality of cam grooves. Referring to FIG. 1, for example, a cam frame 21 has three identical sets of cam grooves. The first set of cam grooves includes a first cam groove 215, a second cam groove 214 and a third cam groove 213. The second set of cam grooves includes a first cam groove 215′, a second cam groove 214′ and a third cam groove 213′. The third set of cam grooves includes a first cam groove 215″, a second cam groove 214″ and a third cam groove 213″.
To introduce the pins (not shown) of lens groups into the cam grooves, the first set of cam grooves has an introducing groove 211 connecting the first cam groove 215, the second cam groove 214 and the third cam groove 213. Similarly, the second set of cam grooves has an introducing groove 211′ connecting the first cam groove 215′, the second cam groove 214′ and the third cam groove 213′, and the third set of cam grooves has an introducing groove 211″ connecting the first cam groove 215″, the second cam groove 214″ and the third cam groove 213″. By such arrangements, the pins of each lens groups can be guided by the introducing grooves 211, 211′ and 211″ to engage the third cam grooves 213, 213′, 213″, the second cam grooves 214, 214′, 214″ and the first cam grooves 215, 215′, 215″.
As shown in FIG. 1, the first set of cam grooves 215, 214 and 213 are formed in region Z1, the second set of cam grooves 215′, 214′ and 213′ are formed in region Z2 and the third set of cam grooves 215″, 214″ and 213″ are formed in region Z3. The regions Z1, Z2 and Z3 do not overlap each other.
Zoom lens is developed to have higher lens magnification, which requires larger displacements of each lens groups in zooming operation. To achieve this, increased lengths of the cam grooves and overlapped regions Z1, Z2 and Z3 are required. However, the cam grooves in one region may interfere the introducing groove in another region. For example, when the region Z1 overlaps the region Z2, the first set of cam grooves 215, 214 and 213 in the region Z1 may interfere the introducing groove 211′ that influences movements of the pin of the lens group in zooming operation.